1. Field of the Invention
This invention concerns a containment tank assembly providing an inner tank which nests within an outer containment vessel designed to avoid spills due to leakage of liquid stored therein. The containment tank assembly is capable of use in environments subject to high winds and seismic disturbances, while providing ease of discharging and filling.
2. Description of the Prior Art
Storage of liquid in bulk is well known, and has evolved in importance due to environmental concerns over the escape of chemicals. In the past, it was common to store chemicals underground in large tanks where gravity was used to fill the vessels and the contents were periodically pumped for use. However, the problems associated with leaking underground storage tanks has increased the usage of above ground storage tanks. Typically, one or more above-ground vessels have been placed in a xe2x80x9ctank farmxe2x80x9d where a concrete pad and berm help to contain and capture any leakage. However, even in these circumstances, leakage from a tank has proved a problem. Rainwater received in the containment area must be monitored and treated if leakage is detected. This has proven very expensive, as the rainwater represents a large volume of liquid even though the leakage is isolated.
As a result, storage containers have been developed which include a double walled construction. Examples of containment tanks utilizing such construction are shown in U.S. Pat. Nos. 5,287,986 to Frost and U.S. Pat. No. 5,333,752 to Harding, Jr. While the double walled construction therein is an improvement over single walled tanks, they require filling and discharge to be accomplished from atop the tanks. This requires extra energy to be expended in pumping the liquid. Moreover, the construction of such tanks is not adapted for utilization in areas where high winds and seismic disturbances may cause violent shifting or sloshing of the contents. Thus, there has developed a need for a containment tank assembly which is capable of use in a variety of environments, minimizes, leakage, and has reduced energy demands.
These objects have largely been met by the containment tank assembly of the present invention. That is to say, the containment tank assembly hereof not only improves resistance to leakage, but permits the contents of the tank assembly to be discharged by gravity. Furthermore, the tank assembly hereof is highly stable even when filled to capacity, and thus resistant to turnover and consequent leakage during seismic events. The containment assembly includes an inner tank and an outer vessel which are formed separately and which nest together, permitting expansion and contraction of the tank and vessel in both vertical and horizontal dimensions independently of one another, thereby reducing the likelihood of fatigue or fracture due to stress.
Broadly speaking, the containment tank assembly hereof includes an inner tank which is configured to nest within an outer containment vessel. A discharge outlet is provided with a sealing boot, whereby liquid within the inner tank may be discharged through the outer containment vessel without leakage therein. The inner tank includes lugs at circumferentially spaced intervals around the upper edge which may receive tie-die cables for securement of the tank assembly to anchors on the pad or other supporting surface. The inner tank has a sidewall which includes an upper section and a lower section and a connecting drain lip. The lip includes at least one and preferably a plurality of chutes which are received in corresponding notches in the outer vessel. This both provides additional structural support for the inner tank, locate the inner tank in proper alignment with the outer vessel, and allow liquid collected within the lip of inner tank to drain down into the central cylindrical section for discharge from the inner tank. This not only aids in preventing spillage, but also helps to ensure that all of the useful contents of the inner tank may be used rather than wasted.
The inner tank has a preferably cylindrical lower section and an enlarged. upper section with a roof thereover, preferably continuously formed by rotational molding. The roof serves a cover over the inner tank and extends radially outwardly of the uppermost portion of the containment vessel, aiding in shedding rainwater and thus avoiding the intrusion of liquid between the inner tank and outer vessel. The lower section and upper section are connected by the lip as noted above. Advantageously, the outer vessel is molded with an open upper edge with one or a plurality of notches therein. The outer vessel is uniquely configured with a substantially cylindrical upper wall continuous with a lower wall having a plurality of chord sections and arcuate sections when viewed in plan. The chord sections are sized and configured to tangentially engage the outer surface of the lower section of the inner tank in a plurality of engagement areas, thereby enhancing the seismic and wind resistance performance of the assembly without the need for additional spacer blocks or other protrusions between the outer vessel and the inner tank. As a result, the inner tank is further restrained against movement relative to the outer vessel and the molding of the outer vessel may be facilitated.
The containment tank assembly hereof facilitates the use of optional accessories such as a leak detection system. A probe may be placed between the inner tank and the outer vessel with an indicator visible from outside the outer vessel. If no liquid is collected in the containment area therebetween, then rainwater may be permitted to runoff without treatment as there is an affirmative indication that no leakage has occurred. A level indicator and fill pipe assembly advantageously utilizes the double wall construction to permit filling of the inner tank from the side of the assembly rather than from the roof. Additionally, in especially cold environments, insulation or heater elements may be placed between the inner tank and outer vessel to provide indirect heating of the liquid contents of the inner tank.
These and other advantages will be readily appreciated by those skilled in the art with reference to the detailed description and drawings which follow.